Transport networks are typically required to support transmission of different protocols across them. Multi-protocol support is therefore required across Ethernet packet-switched networks. Pseudowire (PW) is one such industry-accepted mechanism for transferring information across a packet-switched network (PSN). Often identified with the protocol for forwarding packets, examples of PSNs include, but are not limited to, Internet Protocol (IP), Layer-Two Tunneling protocol (L2TP), Ethernet, and MPLS (Multi-Protocol Label Switching) networks. In general, a PW emulates the attributes of a native service supported across the PSN. In effect, a PW decouples the native service, i.e., the protocols and applications, from the underlying facilities that carry the service. The types of emulated services that may be carried by a PW include, but are not limited to, Asynchronous Transfer Mode (ATM), Frame Relay (FR), Point-to-Point Protocol (PPP), High Level Data Link Control (HDLC), Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH), X. 25, TDM (Time Division Multiplexing), DSL (Digital Subscriber Line), and Ethernet.
FIG. 1 shows a prior art implementation of a communications network 10 in which a PW 12 is established between an ingress provider edge (PE) 14 and an egress provider edge (PE) 16. The PW 12 emulates a native service (e.g., ATM, Ethernet, Frame Relay, T1/T3, etc.) across a PSN 18. Each PE 14, 16 is in communication with at least one customer edge (CE) device 20 (each of which are part of a customer network). Each CE 20 communicates with a PE 14, 16 through an attachment circuit (AC), which is, generally, a physical or logical circuit configured for the particular technology of the native service.
Industry has devised various mechanisms for establishing PWs to carry different native services over MPLS and IP networks. Such mechanisms typically involve “normalizing” payload of the native service for transmission through the PW over the PSN. One technique for normalizing payload is an MPLS encapsulation, referred to as Martini-encapsulation, which uses a control word to distinguish PW payload from standard IP payload. In general, a control word is an optional header used in some encapsulations to carry per-packet information. Bryant, S. et al, in “PWE3 Control Word for use over an MPLS PSN”, October 2005, describes the use of control words in MPLS PSNs for such purpose. Such encapsulation entails the use of a label (referred to as a Virtual Circuit (VC) label or as PW label) for providing a demultiplexer for the PW through the PSN tunnel, e.g., a Label-Switched Path (LSP).
In addition to MPLS and IP PSNs, Ethernet is fast emerging as a viable PSN technology and becoming more widely used, particularly in metro-area networks. Besides being able to offer Ethernet connectivity services, e.g., E-Line, E-LAN, and E-Tree, multi-protocol transport is also a requirement across Ethernet PSNs. Even with the IP and MPLS PSNs, service providers have a limited number of mechanisms to choose from by which they can perform fault detection and diagnostics in order to verify the connectivity of their multi-protocol transport services via PWs. Current mechanisms, such as ICMP (Internet Control Message Protocol) ping, BFD (Bidirectional Forwarding Detection), and MPLS ping, provide only limited OAM (Operations, Administration, & Maintenance) functionality. Moreover, such mechanisms are unduly complicated and have limited application in certain network environments. For instance, current mechanisms do not support verifying the end-to-end connectivity of multi-segment PWs. Thus, there is a need for improving current fault detection and diagnostics mechanisms for single segment and multi-segment PWs including their use in Ethernet PSNs.